The logs in the bags will be standard length(30cm) and range from about about 5cm to 20cm in diameter. Round logs burn longer than split wood. If you split a 10cm log into 2,this would burn quicker than the same size log which isn’t split. This is due to less surface area exposed to the fire. When logs are split,we multiply the surface area exposed to the fire, hence burning faster. Use the split wood to get your fire up and burning hot and then throw a log onto it,which will slow down the burn. Your fire must be up and burning hot ,as if you place the logs on before this, they won’t burn. You might need to mix some split wood in with the round to keep the fire flaming. These logs will vary in wood type but will all be clean burning wood species.
There might be chunkier pieces of split wood and not all round logs but this still has the same affect of slowing the fire burn down.